Similar species: Toxicodendron radicans is a vine or shrub with aerial roots, narrower leaflets, and an open cluster of fruit hainging downward. The hybrid between Toxicodendron radicans ssp. negundo and Toxicodendron rydbergii is intermediate in characteristics, and can be distinguished from T. rydbergii because it sometimes grows as a vine or has aerial roots, occasionally has somewhat hairy leafstalks, and has narrower leaflets. A few tree and shrub species may be mistaken for T. rydbergii. Acer negundo and Staphylea trifolia have opposite leaf arrangements. Ptelea trifoliata has alternate leaves, but the leaflets are all very short-stalked with non-toothed to finely toothed margins.

Flowering: late May to late June

Habitat and ecology: A northern and western species found scattered in fields, woods, dunes, and open, sunny areas.

Occurence in the Chicago region: native

Notes: Avoid touching this plant, as it contains a toxic compound called urushiol. Do not burn it, as the toxin is released into the air and can be inhaled. After contact with urushiol, a person sesitive to the toxin becomes itchy, and within 24 - 48 hours the skin blisters and reddens. If tools or clothing have been contaminated, they should be washed with hot water and soap.

Etymology: Toxicodendron means "poison tree." Rydbergii is named after Per Axel Rydberg, an early 20th century member of the New York Botanic Garden and expert on the flora of the western United States.

Vigorously rhizomatous and colonial, suberect, simple or sparingly branched shrub to 1(-3) m; lvs tending to be approximate toward the top of the stem; petioles elongate, glabrous; lfls broadly ovate to suborbicular, tending to be openly folded along the midrib rather than flat, glabrous on both sides, or strigose beneath and often with a line of minute, curly hairs along the midrib above; infl unbranched (racemose) or sparingly branched, usually with fewer than 25 fls; frs 4-7 mm thick, smooth, sessile or subsessile and crowded in a ±erect infl; otherwise much like no. 4 [Toxicodendron radicans (L.) Kuntze], with which it intergrades to some extent; 2n=30. Open, sunny habitats; widespread in w. U.S., extending e. in n. U.S. (especially north of the 42nd parallel) and s. Can. to N.S. and N.Y., thence s. at upper elev. to Va. and W.Va.